no i haven't but i think a pitch black room with no lights on in the middle of the night is pretty much the same thing as far as lighting conditions go.

From what I read the distance of the object lit by the af assist seems to have a significant impact on the focusing ability, next to the lens used... and your "pitch black" setup might sound like a worst case scenario, but not that's necessarily true because in real life the camera has to deal with varying combinations of af and real light.

no i haven't but i think a pitch black room with no lights on in the middle of the night is pretty much the same thing as far as lighting conditions go.

From what I read the distance of the object lit by the af assist seems to have a significant impact on the focusing ability, next to the lens used... and your "pitch black" setup might sound like a worst case scenario, but not that's necessarily true because in real life the camera has to deal with varying combinations of af and real light.

good point. I was focusing on something about 5 ft in front me. I was able to see the AF beam through the camera because it was so dark and the red really stood out.... and yes, when I say pitch black, I mean pitch black. no street lights shining in through a window... nothing. pitch BLACK.

so anyways, i tested again with as much distance as I could in the same room... the longest dimension of the room is about 30 feet so I just pointed at the wall 30 ft away, even though i couldn't see a damn thing, waited for focus, and shot.... AF worked fine, like I was in a well lit room. the wall was far enough away that I sure as hell couldn't see the AF beam on it. Focus was fine.

I have other thoughts on variables that might be tripping people up:

1) what lenses are we having issues with? I used both the 24-70 2.8 II and the 70-200 2.8 IS II... both at 2.8 when I did my "testing". Maybe f/4 lenses are having a harder time seeing the AF beam in low light.

2) Also, would the color/pattern of what you are focusing on in low light contribute to the camera having a hard time. For example, if the subject was RED in color, or even had something with red tones in it, maybe there wasn't enough contrast between the subject and the AF beam from the 600.

3) Maybe the problem is in the speed lights and not the 5D mk3. Low batteries maybe? maybe without fresh batteries, the AF assist beam isn't bright enough. or maybe some of the new 600 ex-rt units (remember those are new too) have issues

I'm just trying to find a way to re-create the issue that people are having. There's obviously enough of a problem (or two) with this combo that a lot of people are noticing a significantly slower focus speed. I for one cannot re-create the problem. I swear, it's just about as fast as if i was focusing in broad daylight.

Can any of the other people who have the issue reply with the lenses they've used, the subject/color they're shooting, and try it with different speed lights with fresh batteries?

Have you used it in a live situation yet? Dark venue like a wedding reception or another event.

Also, I just realized that I shot at my cousin's wedding on 12/30/12 with my gear. It wasn't a paid gig for me so it didn't come to mind when I replied. I just shot for fun while the hired photographer did the actual work.

yes it was dark on the dance floor. yes, I used my mk3 and 600 (and an addtl of camera flash). No, I didn't feel any lag in the AF.

no i haven't but i think a pitch black room with no lights on in the middle of the night is pretty much the same thing as far as lighting conditions go.

From what I read the distance of the object lit by the af assist seems to have a significant impact on the focusing ability, next to the lens used... and your "pitch black" setup might sound like a worst case scenario, but not that's necessarily true because in real life the camera has to deal with varying combinations of af and real light.

good point. I was focusing on something about 5 ft in front me. I was able to see the AF beam through the camera because it was so dark and the red really stood out.... and yes, when I say pitch black, I mean pitch black. no street lights shining in through a window... nothing. pitch BLACK.

so anyways, i tested again with as much distance as I could in the same room... the longest dimension of the room is about 30 feet so I just pointed at the wall 30 ft away, even though i couldn't see a damn thing, waited for focus, and shot.... AF worked fine, like I was in a well lit room. the wall was far enough away that I sure as hell couldn't see the AF beam on it. Focus was fine.

I have other thoughts on variables that might be tripping people up:

1) what lenses are we having issues with? I used both the 24-70 2.8 II and the 70-200 2.8 IS II... both at 2.8 when I did my "testing". Maybe f/4 lenses are having a harder time seeing the AF beam in low light.

2) Also, would the color/pattern of what you are focusing on in low light contribute to the camera having a hard time. For example, if the subject was RED in color, or even had something with red tones in it, maybe there wasn't enough contrast between the subject and the AF beam from the 600.

3) Maybe the problem is in the speed lights and not the 5D mk3. Low batteries maybe? maybe without fresh batteries, the AF assist beam isn't bright enough. or maybe some of the new 600 ex-rt units (remember those are new too) have issues

I'm just trying to find a way to re-create the issue that people are having. There's obviously enough of a problem (or two) with this combo that a lot of people are noticing a significantly slower focus speed. I for one cannot re-create the problem. I swear, it's just about as fast as if i was focusing in broad daylight.

Can any of the other people who have the issue reply with the lenses they've used, the subject/color they're shooting, and try it with different speed lights with fresh batteries?

I use the 70-200 f/2.8L IS II and it is the lens I have the most issues with. I have shot 20+ weddings with that lenes two 5D3s and 3 600ex flashes. I have been in a lot of different lighting conditions. What I don't like is that the AF assist beam makes focus worse in most cases. When it is very dark or even black then the AF assist helps and I don't have as many issues. I have found that there are surfaces that absorb more light that make the af assist almost useless. For example if the bride and groom are dancing then I focus on lighter areas like her dress or faces. If I miss and focus on a black tux then there is not hope for the AF assist it is just absorbed by the tux. My problem is that when it is dark but not very dark the lens and camera focus better without the AF assist. I have done it a 100 times where I have attempted focus and the AF assist beam will blink 3 full times before I can get a focus lock. When I turn off the AF assist beam the camera focuses instantly on the same thing in the same light. These lighting conditions are frustrating because it can range to light enough for no AF assist to pitch black and needing the AF assist in seconds and I am stuck messing with my settings and turning on the AF assist for 10-15 seconds. In that time I may have missed something important. Instead I would like to keep it on all of the time instead of switching it on and off. If I leave it on all of the time I am stuck with the frustrating 2-3 AF assist blinks while the camera locks focus. I have found a way around that where I have set the camera up to release priority instead of focus priority so it will allow me to take the picture before the red confirmation blink. 90% of the times those shots are in focus but there is always a chance it isn't and I am afraid that I may miss something important especially at a wedding if I rely on it to be focused before it says it is.

Considering the amount of posts and information that is already here in this thread and several other threads, what do you think the chances are that someone from Canon that is reading the posts on the Canon forum might simply click over and read the CR threads if the links are posted on their forum? Just sayin'...

Considering the amount of posts and information that is already here in this thread and several other threads, what do you think the chances are that someone from Canon that is reading the posts on the Canon forum might simply click over and read the CR threads if the links are posted on their forum? Just sayin'...

Personally I doubt the really important people who could actually fix things (i.e. the Japanese devs) read the US Canon forum either - with the lack of easy reproducibility some really important photog or tester would have to step on their toes so they actually try to provoke the problem, otherwise the "don't ask, don't tell" solution comes to mind... some mod in the Canon forum writing some comforting words imho doesn't mean anything.

Agreed. As long as Canon sees strong sales numbers and plenty of good press for the 5D3, I'll be amazed if this is addressed in any major way. If there was some bad press and sales were off, heads would be rolling and 5D3 repairs would be a priority. I'm afraid it's likely that simple. I would love to be wrong and see some major changes in the next firmware release!!

I would love to be wrong and see some major changes in the next firmware release!!

The next 5d3 firmware release is scheduled for sometime in April (2013 afaik :-)) - maybe they'll do a silent fix by then, let's wait and see ... but I've decided to save the €1000 and get a 6d anyway, so for me it's more like general interest in Canon reacting or not.

I would love to be wrong and see some major changes in the next firmware release!!

The next 5d3 firmware release is scheduled for sometime in April (2013 afaik :-)) - maybe they'll do a silent fix by then, let's wait and see ... but I've decided to save the €1000 and get a 6d anyway, so for me it's more like general interest in Canon reacting or not.

That's what I ended up doing, and mostly for this low light focus issue. The IQ is great, and I have not noticed any hardship at all from not having 200 AF points. This thing will grab focus (with a nice red square and a cheerful beep) of scenes where it is so dark that the actual image is 99% black even with ISO cranked up to 10k. I also used a portion of the savings to scoop up an EF 85mm f/1.8 which I am really enjoying too.

I also used a portion of the savings to scoop up an EF 85mm f/1.8 which I am really enjoying too.

Well, this is off topic, but I'm putting the saved money into a 17-40L, a flash bracket/diffuser and nd + polarizer filters that are incredibly expensive for 82mm - after long considerations that should result in better (at least more versatile) pictures than getting the most shiny camera body which is like burning cash.

But I wish everyone with a 5d3 luck solving this problem, if Canon should really ignore things like this and get away it's not good for any Canon shooter.

Well, I sorta did it all. I waited years for the 5D3, bypassed the 5D2 and still love the 5D anyway. I built up my lens collection and other needed accessories. I took a gillion pictures and honed my skills. I waited until a great deal on a 5D3 popped in Nov and got one. Promptly exchanged it for another to get better but not mind blowing low light AF. Got a 6D in Dec for another killer deal and now have much improved low light AF. For shooting the swim team, the 5D3 is still better, higher frame rate, etc. But otherwise, (and partly the reason I said all this) I plan to wait until the next firmware release and then sell the 5D3 if there isn't a big improvement. If the 5D3 blows me away I'll sell the 6D. Either way I'll know a lot about both bodies by then and in the meantime, I'm probably going to start selling a few other things. This whole experience with the 5D3 has made me re-think how much I'm spending on this hobby and along with the sky high lens prices coming out lately, my "circuit breaker" is starting to trip. Time to dial back and concentrate on taking pictures again, not on spending money and talking about it. Know what I mean?

On the topic of selling, I sure wish CR would start a "market section" for members to buy/sell. eBay is way too risky now to sell stuff. Way too many scammers out there now using eBay and PayPal Buyer Protection to basically steal honest sellers stuff. But I digress....

Considering the amount of posts and information that is already here in this thread and several other threads, what do you think the chances are that someone from Canon that is reading the posts on the Canon forum might simply click over and read the CR threads if the links are posted on their forum? Just sayin'...

I think a major issue is this has been basically ignored at both DPreview and Fred Miranda. DPreview has surprised me as they usually latch on to these things like a Pit Bull. Big players in online forums with little noise so far. Does not help this cause.